Stem cells can divide to form new stem cells and to differentiate into specific cells, for example, tissue-specific cells. This makes them valuable for the repair or replacement of damaged tissues and structures which have been widely discussed. But growth of most eukaryotic animal cells, such as human cells, requires environments including surfaces to permit them to grow. A challenge in engineering tissues is mimicking the three-dimensional organization and function of living animal tissues such as the human body.
Three-dimensional extracellular matrices have been constructed in laboratories to provide an artificial environment for cells that better mimic the physical arrangement, cellular organization, and gene expression of living tissues than two dimensional cultures such as Petri dishes. Cells in collagen gels have demonstrated that cells can express natural organization and differentiation, cell-cell interactions, gene expression, and aspects of natural histology.
The manufacture of complex tissue scaffolds presents challenges. Typically, bulk properties of a matrix are adjusted so that the entire cell population can be modulated. However, such bulk changes may not be appropriate when trying to recreate the complex three-dimensional (3D) patterning, organization and regional architecture of one or more cell types in an engineered tissue construct. In such cases, techniques for controlling the local microenvironment presented to specific cell populations within a 3D construct may be desired. Even relatively simpler tissue scaffolds, such as for artificial skin applications present difficult challenges in terms of providing mechanical support, sufficient integrity to allow manipulation, while permitting host cell ingrowth.
Naturally-derived extracellular matrices (ECMs) can be used in tissue engineering, drug delivery applications and basic biological studies, due to their close resemblance (in structure and composition) to in vivo ECM. In particular, constructs can be formed into three-dimensional (3D) ECMs so as to mimic the often inhomogeneous and anisotropic properties of native tissues and to construct in vitro cellular environments. Since these 3D ECMs provide physiologically relevant cellular environments, they can be used to study tissue morphogenesis and to engineer tissue.